User & has not been assigned to a forwarding agent

What causes this issue?

For reasons of security, a user must be assigned for verifications and
confirmations of transportation events to each forwarding agent who
performs a verification.

How to fix this error?

Assign a user for each forwarding agent who wants to verify or confirm
transportation events in the IMG using <DS:TRAN.OVTVT_CA>Configuration
of Transportation Planning for Forwarding Agents</>.

Error message extract from SAP system. Copyright SAP SE.